Hugo Barra, vice president of product management for Android at Google Inc., listens during a presentation at the Google I/O Annual Developers Conference in San Francisco. Google Inc. introduced its subscription music-streaming service Wednesday.

SAN FRANCISCO — Google Inc. unveiled a streaming music service called All Access that blends songs users have already uploaded to their online libraries with millions of other tracks.

Google made it available in the U.S. Wednesday for $8 a month to early birds who sign up for service before June 30.

In addition to a 30-day free trial, the offer shaves $2 off the price of popular paid subscription plans from Spotify and Rhapsody. The service is an attempt by the world’s dominant Internet company to carve itself a bigger piece of the digital music pie as more people listen to streaming music on mobile devices.

The announcement Wednesday at Google’s annual developers conference in San Francisco kicks off a wave of developments as technology giants go beyond core music fans and look to entice more casual listeners.

Rival Apple Inc. is expected to debut a digital radio service later this year that will drive more people to its iTunes music store; Google-owned YouTube is also working on a paid subscription music plan with a deeper catalog of songs than it has now; and Sweden’s Spotify is exploring a way to make a version of its paid streaming plan free with ads on mobile devices, according to a person in the music industry familiar with the matter.

The person was not authorized to speak publicly about the developments because the deals and features on the services have not been finalized.

Google is playing catch-up in the digital music space after launching its music store in November 2011.

A customer dining at Washington’s Oceanaire restaurant noticed an unusual line at the bottom of his receipt: “Due to the rising costs of doing business in this location, including costs associated with higher minimum wage rates, a 3% surcharge has been added to your total bill.”